The uptake of exogenous tritiated norepinephrine (H3-NE) by the cardiovascular blood vessels of spontaneously hypertensive rats (AHR) and normotensive Wistar Kyoto (WKy) rats are being investigated. The isolated tissues are incubated with H2-NE and the storage vesicles are isolated by means of sucrose density gradient centrifugation. Studies of H3-NE incorporation into the isolated storage vesicles indicate that the atria synaptic vesicles of 12 week old SHRs take up less H3-NE than those of WKy rats (approximately 50 to 95% of WKy rats), and as do the portal-mesenteric veins of SHRs, (33 to 88% of WKy) rats. The mesenteric artery of SHR, on the other hand, show a higher level of NE uptake as compared to those WKy rats. These results indicate that the neurotransmitter uptake is different on the low and high pressure sides of the circulatory system.